IEEE 802.11 RTS/CTS

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RA - Receiver Address indicating the MAC Address of the station that shall receive frame.
TA - Transmitter Address indicating the MAC address of the station which has transmitted frame.
FCS - Frame Check Sequence.

This protocol was designed under the assumption that all nodes have the same transmission ranges, and does not solve the hidden terminal problem. The RTS/CTS frames can cause a new problem called the exposed terminal problem in which a wireless node that is nearby, but is associated with another access point overhears the exchange and then is signaled to backoff and cease transmitting for the time specified in the RTS.

RTS/CTS packet size threshold is 0–2347 octets. Typically, sending RTS/CTS frames does not occur unless the packet size exceeds this threshold. If the packet size that the node wants to transmit is larger than the threshold, the RTS/CTS handshake gets triggered. Otherwise, the data frame gets sent immediately.

IEEE 802.11 RTS/CTS mechanism could help solve exposed node problem as well, only if the nodes are synchronized and packet sizes and data rates are the same for both the transmitting nodes. When a node hears an RTS from a neighboring node, but not the corresponding CTS, that node can deduce that it is an exposed node and is permitted to transmit to other neighboring nodes.[1] If the nodes are not synchronized (or if the packet sizes are different or the data rates are different) the problem may occur that the exposed node will not hear the CTS or the ACK during the transmission of data of its neighbor.